Transferring nanofiber forests between substrates

Abstract

Techniques are described for transferring nanofiber forests using transfer films that either lack a conventional adhesive at the substrate—nanofiber forest interface or that include a diffusion barrier that prevents diffusion of adhesive molecules (or other polymer molecules mobile at ambient temperatures) into the nanofiber forest. These techniques can be applied to single layer nanofiber forests or stacks of multiple nanofiber forest. By selecting the bond strength between the nanofiber forest and the transfer films, the nanofibers can be aligned in a common direction that includes, but is not limited to, perpendicular to a substrate or transfer film.

What is claimed is: 
     
       1. A nanofiber assembly comprising:
 a first adhesive-free transfer film with a non-adhesive coating; and 
 a nanofiber forest comprising a plurality of nanofibers, the nanofiber forest being physically bonded to the first adhesive-free transfer film and free of adhesive. 
 
     
     
       2. The nanofiber assembly of  claim 1 , wherein the first adhesive-free transfer film comprises an elastomeric polymer. 
     
     
       3. The nanofiber assembly of  claim 1 , wherein the non-adhesive coating is paraffin wax. 
     
     
       4. The nanofiber assembly of  claim 1 , further comprising a second adhesive-free transfer film physically bonded to a surface of the nanofiber forest opposite the first adhesive-free transfer film, wherein the first adhesive-free transfer film has a first bond strength greater than a second bond strength of the second adhesive-free transfer film. 
     
     
       5. The nanofiber assembly of  claim 4 , wherein the first adhesive-free transfer film, the second adhesive-free transfer film, and the nanofiber forest are wound into a roll. 
     
     
       6. The nanofiber assembly of  claim 4 , wherein the first bond strength is less than 2 Newtons/25 mm and the second bond strength is greater than 2 Newtons/25 mm. 
     
     
       7. The nanofiber assembly of  claim 1 , wherein the nanofibers of the forest are aligned in a common direction from 0° to 5° to a proximate surface of the first adhesive-free transfer film. 
     
     
       8. The nanofiber assembly of  claim 1 , wherein the nanofiber forest comprises two or more stacked nanofiber forests. 
     
     
       9. The nanofiber assembly of  claim 1 , wherein the nanofibers of the nanofiber forest comprise a straight portion, an arcuate portion, and an angled portion between the straight portion and the arcuate portion. 
     
     
       10. A method of forming a nanofiber assembly, the method comprising:
 providing a first transfer film comprising a non-adhesive coating and having a first bond strength; 
 providing a nanofiber forest comprising a plurality of nanofibers free of adhesive having a first surface and a second surface opposite the first surface; and 
 applying the first transfer film to the first surface of the nanofiber forest to form a nanofiber assembly comprising the first transfer film bonded to the nanofiber forest. 
 
     
     
       11. The method of  claim 10 , further comprising:
 providing a second transfer film free of adhesive and having a second bond strength greater than the first bond strength; and 
 applying the second transfer film to the second surface of the nanofiber forest. 
 
     
     
       12. The method of  claim 11 , further comprising:
 applying a compressive force to the first transfer film and the second transfer film; and 
 responsive to the applied compressive force, causing straight portions of the nanofibers of the nanofiber forest to become aligned in a common direction from 0° to 5° relative to a proximate surface of at least one of the first transfer film and the second transfer film. 
 
     
     
       13. The method of  claim 11 , further comprising winding a length of the first transfer film, the second transfer film, and the nanofiber forest therebetween into a roll. 
     
     
       14. The method of  claim 11 , wherein the nanofibers of the nanofiber forest comprise open ends and tangled ends. 
     
     
       15. The method of  claim 14 , further comprising:
 removing one of the first transfer film or the second transfer film to expose the first surface or the second surface of the nanofiber forest; and 
 placing the exposed first surface or second surface of the nanofiber forest on a final substrate. 
 
     
     
       16. The method of  claim 15 , wherein the final substrate comprises an adhesive layer used to adhere the nanofiber forest that is free of adhesive to the final substrate. 
     
     
       17. The method of  claim 15 , further comprising removing a remaining one of the first transfer film and the second transfer film, the removing causing the plurality of nanofibers of the nanofiber forest to orient in a common direction greater than from 0° to 5° from a surface of the final substrate. 
     
     
       18. The method of  claim 12 , further comprising winding a length of the first transfer film, the second transfer film, and the nanofiber forest therebetween into a roll. 
     
     
       19. The method of  claim 12 , wherein the nanofibers of the nanofiber forest comprise open ends and tangled ends. 
     
     
       20. The method of  claim 18 , further comprising:
 removing one of the first transfer film or the second transfer film to expose the first surface or the second surface of the nanofiber forest; and 
 placing the exposed first surface or second surface of the nanofiber forest on a final substrate.